In an invention disclosed in PTL 1, a physical package included in a slave main device is used as a package for controlling a digital terminal and a digital line. The physical package included in the slave main device uses a correspondence table to be associated with a virtual slot included in a master main device. Then the master main device utilizes the association to thereby control the digital terminal and digital line which are connected with the physical package of the slave main device. The physical package included in each slave main device uses a CPU of the corresponding slave main device to control the digital terminal and the like, so that processing for such control can be avoided from being concentrated on a CPU of the master main device.